When using a laser-heating line for printing, ink drying, roll to roll manufacturing processes or other applications the object to be heated at the surface passes below the heating line in a direction perpendicular to the line direction. Alternatively, the heating line is moved in the direction perpendicular to the line direction relative to the object. In order to generate a laser line of sufficiently high laser power with semiconductor lasers it is necessary to arrange several sub-modules carrying arrays of surface emitting semiconductor lasers side by side on a common carrier. The emission of the single semiconductor lasers is then focused by an appropriate lens system, in particular a cylindrical lens to the desired line shape on the working plane. With such a module problems arise due to the unavoidable gap between the individual sub-modules which results in several intensity minima along the laser line. To avoid or reduce such intensity minima WO2011/21140 A2 proposes a special design of the optics for focusing the laser radiation onto the working plane which overlaps the intensity distributions of adjacent sub-modules along the laser line. Optical gaps between two sub-modules can then be closed for certain distances between the module and the working plane.